To carry out the present day precision in lathe work it is essential that the jaw faces which bear against the work accurately define a circle which is in absolute axial alignment with the axis of the work piece. This can be achieved by individually adjusting the jaws radially back and forth until the work is positively positioned in its intended location, but this is a very time consuming and tedious task. The working time which is lost in such a procedure is totally inconsistent with high productivity.
Various short cuts have been devised to shorten the setup time to accurately position the work piece and one of these ways is to provide the jaws with so-called soft material which can relatively easily be machined. This soft material makes it possible to rotate the chuck on the lathe in a normal manner and machine the soft material to absolutely accurate concentricity to receive the work. However, even this has its limitations as the slight slack which exists between the operating parts of the chuck mechanism results in a more or less malpositioning of the jaws.